"Green Archer" at RAF Salalah

Radar, Field Artillery, No 8, better known as Green Archer, was a widely British mortar locating radar operating in the X Band using a Foster scanner. It was in British service from 1962 until 1975 with the Royal Artillery. It was developed by EMI after an experimental model by the Royal Radar Establishment Green Archer comprised two units each mounted on a four wheel trailer with levelling jacks, one unit was the complete radar, the other a fully silenced generator inaudible at 200 m to permit operation in forward areas. The radar unit weighed 2,915 kg and with the antenna in the operating position was 2.9m high.

Green Archer’s distinguishing characteristic was its Foster scanner. This converted the conic radar beam into one some 40° wide in azimuth and less than 1° high in elevation. The antenna was mechanically switched between two fixed elevations. The radar detected a mortar bomb as it passed through the lower beam, the operator marked it on his display and flicked the beam into the upper elevation, and again marked the bomb as it went through the beam. He then placed cursors over his marks and input the plot to the radar’s analogue computer.

These two plots, the time between them and the angle between the two beam positions gave two points on a parabolic curve (which is defined by two points and is a good approximation of a mortar bomb trajectory). Using these, the azimuth of the radar beam centre and the radar’s coordinates, the mortar position coordinates were calculated. These could be adjusted to reflect the actual height of the ground.

Green Archer could locate a medium mortar up to about 10km away and a heavy mortar out to 17 km. It took about 30 secs from a mortar firing to producing its location. The radar could also be used ‘in reverse’ to observe and adjust mortar fall of shot and that of guns firing in high angle. It was also capable of surface observation.

These details are taken from Wikipedia